Nadezda Koleganova

A calcimimetic (R-568), but not calcitriol, prevents vascular remodeling in uremia

Renal insufficiency increases cardiovascular risk, accelerates atherogenesis, and causes vascular wall remodeling. Here we evaluated the effect of the calcimimetic R-568 and non-hypercalcemic doses of calcitriol on vascular structure. Subtotal nephrectomy was produced in Sprague-Dawley rats followed by treatment with R-568, calcitriol, or vehicle for 12 weeks. The aortic wall was significantly thicker in vehicle-treated uremic rats than in those with a sham-operation but R-568-treated uremic rats had a lower value. In contrast, calcitriol increased wall thickness in both the sham-operated and uremic groups. The calcification score, measured by von Kossa staining, and the number of proliferating cells in the intima and media were significantly higher in the calcitriol-treated uremic group. The expression of the calcium sensing receptor was higher in the intima of sham-operated and uremic rats treated with R-568 compared to animals treated with vehicle or calcitriol, while the expression of the vitamin D receptor was upregulated by both calcitriol and R-568. Our study shows that in uremic rats, calcitriol increased while R-568 attenuated media calcification and proliferation of vascular smooth muscle and endothelial cells.

Arterial calcification in patients with chronic kidney disease

OBJECTIVE In patients with chronic kidney disease (CKD), aortic calcification is more frequent and severe and it is also predictive of adverse cardiovascular outcome. The aim of the present study was to characterize aortic calcification in renal compared with non-renal patients. METHODS Aortas of 31 patients with advanced CKD and of 31 age-and gender-matched controls were obtained at autopsy. Calcium and phosphorus content in the aorta was quantitated using x-ray analysis. The expression of calcification-promoting and calcification-inhibiting proteins was assessed using immunohistochemistry. RESULTS The calcium and phosphorus content of the aorta was higher in CKD patients than in controls. Even in non-calcified aortic specimens of CKD, staining for Msx-2, BMP-2, bone sialo-protein, TNF-alpha and nitrotyrosine was significantly more marked compared to controls. The same proteins were immunodetected in calcified aortic specimens of both CKD and controls. In contrast, staining for transglutaminase-2 and Fetuin A was significantly reduced in CKD. Higher expression of cbfa-1 and Pit-1 was observed in all calcified aortas with no difference between CKD and controls. The expression of TNF-alpha, phospho-p38 and Msx-2 was correlated to the intensity of upregulation of BMP-2 and osteoblastic transdifferentiation by VSMC even in non-calcified areas of the aortas of CKD. CONCLUSION The expression of markers characteristic for calcification is not different in calcified aorta of CKD patients compared to controls, but in CKD patients, evidence of inflammation, transformation to an osteoblastic phenotype and reduced expression of transglutaminase are also found even in non-calcified aorta.

Both high and low maternal salt intake in pregnancy alter kidney development in the offspring

In humans, low glomerular numbers are related to hypertension, cardiovascular, and renal disease in adult life. The present study was designed 1) to explore whether above- or below-normal dietary salt intake during pregnancy influences nephron number and blood pressure in the offspring and 2) to identify potential mechanisms in kidney development modified by maternal sodium intake. Sprague-Dawley rats were fed low (0.07%)-, intermediate (0.51%)-, or high (3.0%)-sodium diets during pregnancy and lactation. The offspring were weaned at 4 wk and subsequently kept on a 0.51% sodium diet. The kidney structure was assessed at postnatal weeks 1 and 12 and the expression of proteins of interest at term and at week 1. Blood pressure was measured in male offspring by telemetry from postnatal month 2 to postnatal month 9. The numbers of glomeruli at weeks 1 and 12 were significantly lower and, in males, telemetrically measured mean arterial blood pressure after month 5 was higher in offspring of dams on a high- or low- compared with intermediate-sodium diet. A high-salt diet was paralleled by higher concentrations of marinobufagenin in the amniotic fluid and an increase in the expression of both sprouty-1 and glial cell-derived neutrophic factor in the offsprings kidney. The expression of FGF-10 was lower in offspring of dams on a low-sodium diet, and the expression of Pax-2 and FGF-2 was lower in offspring of dams on a high-sodium diet. Both excessively high and excessively low sodium intakes during pregnancy modify protein expression in offspring kidneys and reduce the final number of glomeruli, predisposing the risk of hypertension later in life.

Calcitriol ameliorates capillary deficit and fibrosis of the heart in subtotally nephrectomized rats

BACKGROUND Remodelling of the heart, characterized by hypertrophy, fibrosis and capillary/myocyte mismatch, is observed in patients with chronic renal failure. Low vitamin D levels have been associated with increased cardiovascular risk. In the present experimental study, we studied the effects of non-hypercalcaemic doses of calcitriol on microvascular disease and interstitial fibrosis of the heart. METHODS Three-month-old male Sprague-Dawley rats were randomized to subtotal nephrectomy (SNX) or sham operation and received calcitriol (6 ng/kg) or vehicle starting immediately thereafter. Blood pressure was measured by tail pletysmography. Albuminuria was measured by rat-specific ELISA. Capillary length density, volume density of interstitial tissue, immunohistochemistry and western blots (vitamin D receptor, collagen I, III, TGF-beta(1), MAP kinases and nitrotyrosine) were assessed after 12 weeks of treatment. RESULTS After SNX blood pressure, albuminuria and heart weight were elevated, capillary length density reduced and interstitial fibrosis increased. Treatment with calcitriol reduced albuminuria and prevented reduction of capillary density and expansion of interstitium without affecting significant blood pressure and heart weight after perfusion fixation. Calcitriol left high VEGF unchanged, but upregulated VEGF receptor 2 (presumably reversing VEGF resistance). Calcitriol reduced expression of profibrotic TGF-beta(1) and the accumulation of collagens I and III. CONCLUSIONS Non-hypercalcaemic doses of calcitriol ameliorated, directly or indirectly, cardiac remodelling in sub- totally nephrectomized rats.

Calcimimetic R-568 or calcitriol: equally beneficial on progression of renal damage in subtotally nephrectomized rats

Patients with renal insufficiency develop secondary hyperparathyroidism. Monotherapy with active vitamin D or calcimimetics ameliorates secondary hyperparathyroidism. We compared kidney damage in subtotally nephrectomized (SNX) rats treated with active vitamin D (calcitriol) or the calcimimetic R-568. Male Sprague-Dawley SNX and sham-operated (sham-op) rats were randomized into the following treatment groups: SNX + R-568, SNX + calcitriol, SNX + vehicle, sham-op + R-568, sham-op + calcitriol, and sham-op + vehicle. Albuminuria and blood pressure were monitored and kidneys were examined using morphometry, immunohistochemistry, quantitative RT-PCR, and in situ hybridization. Parathyroid hormone concentrations were lowered to the same extent by the two interventions, although phosphorus and the calcium-phosphorus product were reduced only by R-568 treatment. SNX rats developed marked albuminuria, which was significantly reduced in ad libitum- and pair-fed animals treated with R-568 and animals treated with calcitriol. Mean glomerular volume (6.05 +/- 1.46 vs. 2.70 +/- 0.91 mm(3)), podocyte volume (831 +/- 127 vs. 397 +/- 67 microm(3)), the degree of foot process fusion (mean width of foot processes = 958 +/- 364 vs. 272 +/- 35 nm), and glomerular basement membrane thickness (244 +/- 6 vs. 267 +/- 23 nm), as well as desmin staining, were significantly higher in vehicle-treated SNX than sham-operated animals. These changes were ameliorated with R-568 and calcitriol. In SNX, as well as sham-operated, animals, expression of the calcium-sensing receptor (protein and mRNA) was upregulated by treatment with the calcimimetic, but not calcitriol. Calcitriol and R-568 were similarly effective in ameliorating kidney damage.

Is there an obesity-metabolic syndrome related glomerulopathy?

Purpose of reviewThere is an increasing evidence for a specific form of focal segmental glomerulosclerosis (FSGS) related to obesity. Its prevalence has progressively increased in past decades. This form of FSGS represents the tip of an iceberg: a much broader spectrum of renal malfunction is linked to visceral obesity, which is closely connected to, but not completely identical with, the concept of ‘metabolic syndrome’. Recent findingsThe obesity-associated FSGS (obFSGS) is characterized by massive proteinuria and glomerular lesions which are similar to but less pronounced than in idiopathic FSGS, but the long-term prognosis is still dubious.The patholophysiology underlying obesity-associated renal pathology includes insulin resistance and salt sensitivity of blood pressure (BP); more recently adiponectin deficiency, hyperaldosteronism and many other pathogenetic factors have been identified. The abnormalities of renal structure in obese and morbidly obese individuals include increased kidney weight, glomerulomegaly, disorder of podocytes, mesangial expansion and more recently also abnormalities of the renal interstitium. This is accompanied by functional abnormalities, that is renal hyperperfusion, increased filtration fraction and albuminuria. Both obesity and metabolic syndrome have been identified as powerful predictors of chronic kidney disease (CKD) and end-stage renal disease (ESRD). This correlation is not fully explained by associated hypertension and prediabetes/diabetes. SummaryThe link between progressive kidney disease and visceral obesity is of enormous public health importance. Apart from causing obFSGS, obesity aggravates most primary kidney diseases. Beyond standard therapy and weight loss, bariatric surgery has recently emerged as a successful intervention for obFSGS.

Effect of paricalcitol and calcitriol on aortic wall remodeling in uninephrectomized ApoE knockout mice

Despite an only minor reduction in the glomerular filtration rate, uninephrectomy (UNX) markedly accelerates the rate of growth of atherosclerotic plaques in ApoE-/- mice. It has been suggested that vitamin D receptor (VDR) activation exerts an antiproliferative effect on vascular smooth muscle cells, but the side effects may limit its use. To assess a potentially different spectrum of actions, we compared the effects of paricalcitol and calcitriol on remodeling and calcification of the aortic wall in sham-operated and UNX ApoE-/- mice on a diet with normal cholesterol content. Sham-operated and UNX mice were randomly allotted to treatment with solvent, calcitriol (0.03 μg/kg) or paricalcitol (0.1 μg/kg) 5 times/wk intraperitoneally for 10 wk. Semithin (0.6 μm) sections of the aorta were analyzed by 1) morphometry, 2) immunohistochemistry, and 3) Western blotting of key proteins involved in vascular calcification and growth. Compared with sham-operated animals (5.6 ± 0.24), the wall-to-lumen ratio (x100) of the aorta was significantly higher in solvent- and calcitriol-treated UNX animals (6.64 ± 0.27 and 7.17 ± 0.81, respectively, P < 0.05), but not in paricalcitol-treated UNX (6.1 5 ± 0.32). Similar differences were seen with respect to maximal plaque height. Expression of transforming growth factor (TGF)-β1 in aortic intima/plaque was also significantly higher in UNX solvent and UNX calcitriol compared with sham-operated and UNX paricalcitol animals. Treatment with both paricalcitol and calcitriol caused significant elevation of VDR expression in the aorta. While at the dose employed paricalcitol significantly reduced TGF-β expression in plaques, calcitriol in contrast caused significant vascular calcification and elevated expression of related proteins (BMP2, RANKL, and Runx2).

Regression of glomerulosclerosis in subtotally nephrectomized rats: effects of monotherapy with losartan, spironolactone, and their combination

Angiotensin II accelerates and renin-angiotensin system blockade halts progression; blockade with high doses even reverses established glomerulosclerosis. Aldosterone also accelerates progression of glomerulosclerosis, partially independently of angiotensin II. The purpose of this study was to assess the relative ability of an angiotensin receptor type 1 (AT1) blocker, a mineralocorticoid receptor blocker, and their combination to reverse glomerulosclerosis. Sprague-Dawley rats were subjected to subtotal renal ablation (SNX) or sham operation. Eight weeks after surgery, they were either euthanized or allocated to treatment with vehicle, losartan, spironolactone, their combination, or unspecific antihypertensive treatment (dihydralazine) for 4 wk. Renal morphology was evaluated by stereology in tissues obtained using pressure-controlled perfusion fixation. Systolic blood pressure was significantly higher in SNX compared with sham-operated animals and decreased in all treatment groups. Compared with wk 8 after SNX, the glomerulosclerosis index (GSI) had increased further by week 12 in the vehicle- and dihydralazine-treated groups but was significantly lowered in the SNX+losartan as well as in the SNX+losartan+spironolactone groups and had not progressed further in the SNX+spironolactone group. The study confirms the partial regression of established glomerulosclerosis in subtotally nephrectomized rats after high-dose AT1 receptor blockade. Nonhyperkalemic doses of spironolactone prevented the increase but failed to decrease the GSI below the 8-wk level and preserved podocyte numbers. Combining the AT1 blocker with mineralocorticoid receptor blockade failed to further increase the regression of glomerulosclerosis.

Interstitial fibrosis and microvascular disease of the heart in uremia: amelioration by a calcimimetic

In patients with chronic renal failure, the heart undergoes remodeling, characterized by hypertrophy, fibrosis, and capillary/myocyte mismatch. In this study, we observed the effects of the calcimimetic agent R-568 on microvascular disease and interstitial fibrosis of the heart. Three-month-old male Sprague–Dawley rats were randomized to subtotal nephrectomy (SNX) or sham operation and subsequently received vehicle or R-568 under two experimental protocols, one for 1 month and the other for 3 months. Echocardiography, capillary length density, volume density of interstitial tissue, and immunohistochemistry and western blots (calcium-sensing receptor, collagen I and III, transforming growth factor (TGF)-β, mitogen-activated protein kinases, and nitrotyrosine) were assessed. After SNX, weight and wall thickness of the left and the right ventricle were elevated. The ratio of heart to body weight and interventricular septum thickness were not changed by R-568 treatment. The left ventricle fractional shortening (by echocardiography) was lower in SNX; this was ameliorated by R-568. Reduced capillary length density and increased interstitial fibrosis in SNX were improved by R-568, which also reduced the expression of TGF-β, and collagen I and III. The calcimimetic increased the activation of ERK-1/2, normalized p38 and JNK signaling, and prevented oxidative stress. We conclude that lowering parathyroid hormone with a calcimimetic significantly improves cardiac histology and function but not the left ventricular mass in SNX.

Role of Sodium Intake in the Progression of Chronic Kidney Disease

The relation of salt to hypertension and kidney disease had been well known at the turn of the last century, but the importance of salt has been grossly neglected more recently. There is a close link between salt intake and hypertension, as well as partially blood pressure-independent target organ damage including renal disease. In the general population, high salt intake is associated with hypertension and cardiovascular events. Salt loading also increases albuminuria in individuals without primary renal disease and raises excretion of albumin and protein in patients with renal disease. It aggravates proteinuria and glomerulosclerosis and accelerates progression in most animal models of renal damage. The effect of salt restriction cannot be reproduced by treatment with diuretics. Inappropriate increase of intrarenal angiotensin II and increased reactive oxygen species are the major culprits responsible for salt-related renal damage.